Hydrofoil



D. Z. BAILEY Oct. 29, 1968 HYDROFOIL 2 Sheets-Sheet 1 Filed D30. 2, 1966 INVENTOR. DAVID Z. BAILEY V/ML (Md/9mm ATTORN EYS D. z. BAILEY Oct. 29, 1968 HYDROFOIL 2 Sheets-Sheet 2 Filed Dec. 2, 1966 INVENTOR." DAVID -z. B AILEY J45, aw! [gm/113ml ATTORN'EY3 United States Patent 3,407,770 HYDROFOIL David Z. Bailey, Warwick, RI. (P.O. Box 69, East Greenwich, RI. 02818) Filed Dec. 2, 1966, Ser. No. 598,643 6 Claims. (Cl. 114-665) ABSTRACT OF THE DISCLOSURE A submerged-hydrofoil watercraft having an upwardly bowed foil shaped such that substantially only tensile forces are applied in the spanwise direction of the foil, thereby enabling a high aspect ratio to be achieved reducing the drag to lift ratio.

This invention relates to hydrofoil watercraft of the totally submerged foil type and in particular provides a submerged foil structure enabling substantially greater aspect ratios than have heretofore been feasible with submerged foil craft.

The dynamic efliciency of a propelled body in a fluid medium generally is determined by the aspect ratio, e.g., the ratio of the span (wing tip to wing tip dimension) to the chord length (forward edge to trailing edge dimension) of the forwardly moving body. To obtain a high aspect ratio and the high dynamic efliciency associated therewith, it has been proposed that the span of the submerged hydrofoil be extended to its maximum permissible limits by the utilization of additional support struts and thicker hydrofoils to absorb the increased bending moments exerted upon the elongated hydrofoil by the lifting force of the water during running operation. While thicker hydrofoils permit elongated spans and high aspect ratios, they also increase the drag to lift ratio of the hydrofoil in the fluid medium to reduce the dynamic efficiency below optimum. A hyrofoil thickness intermediate the confiicting dimensions necessary for minimum drag and high aspect ratio generally must be accepted as a compromise for design purposes.

It is a primary object of the present invention to provide a submerged hydrofoil construction for hydrofoil craft employing totally submerged foils in which bending moments lengthwise of the span are eliminated, and hence more efficient hydrodynamic design can be employed to reduce the drag to lift ratio and at the same time greater lengths of span can be employed to increase the aspect ratio of the foil.

This and other objects of the invention which will become apparent hereinafter are essentially achieved through the use of a submerged foil positioned between a pair of supports attached to the craft. In accordance with the present invention, the length of the submerged foil between such pair of supports is greater than the lateral spacing between the supports, and the foil assumes, at least under flying conditions, a shape such that the stresses imposed on the foil by the lift exerted on the foil are colinear with the hydrodynamic centerline of the foil, and hence any substantial bending moment cannot exist along the length of the span of the foil. Chordal bending moments will continue to exist, but these moments have no effect on the length of permissible span. It will be apparent that if all the forces of lift exerted along the foil are uniform and normal to the hydrodynamic centerline, the foil will have at least under flying conditions a particircular hydrodynamic centerline. On the other hand, if the foil is designed such that along its length uniform lifting forces are vertical it will be apparent that the hydrodynamic centerline of the foil will have the shape of a catenary curve. In practical construction it is apparent that the height of the center of the foil above its ice supported ends is limited by the permissible depth at the supported ends and the necessary submergence of the higher center position of the foil. Under these conditions, very little difference exists between the shape of an arc of a circle and the shape of a catenary curve. Since more eflicient lift is achieved by having all lifting forces on the foil acting in a vertical manner uniformly along the span, the description hereinafter will generally have reference to the foil as having a catenary shape.

In general there are two distinct mechanisms in which submerged hydrofoils of the present invention can be constructed. The foil thus can be formed with a permanent shape, such that the hydrodynamic centerline approximates a catenary or other desired curve, even at rest. On the other hand, the foil can be formed as a plurality of discrete, articulated sections along the span of the foil, in which case the foil only assumes the catenary or other shape during flight. In the latter case, the foil has the advantage of permitting flexing of the foil along its length during flight to accommodate local vertical water movement and thus integrates the lifting forces along the length of the entire span, while at the same time preventing the development of any bending moments along the length of the span caused by such local vertical movement of water. It will be noted that small bending moments temporarily are exerted in the first case described above (in which the foil is pre-formed to the desired shape) when local vertical movement of water is encountered.

In another aspect of this invention, whether the foil is pre-formed or articulated, it is contemplated that along the length of the foil short period control systems will be employed in the manner of Patent No. 2,773,467 for correcting the angle of attack of the foil at discrete intervals along its length. In a practical manner such short period of controls would have the form of small foils or vanes rigidly secured to the foil either immediately before the leading edge or, preferably, :after the trailing edge of the foil, such that local vertical water movement is sensed and the angle of attack of the immediate section of the foil to which the vane is attached is corrected.

While the attack angle of the submerged foil of this invention can be controlled by a mechanism, such as that disclosed in copending application Ser. No. 546,243, filed Apr. 29, 1966, now US. Patent No. 3,345,968, in another aspect of this invention the attack angle can be controlled by controlling the attack angle of the same foils or vanes used to sense local water movement.

For a more complete understanding of the practical application of this invention, reference is made to the appended drawings in which:

FIG. 1 is a front elevation of a watercraft supported by a submerged hydrofoil in accordance with this invention;

FIG. 2 is a section taken along line 22 of FIG. 1;

FIG. 3 is a section taken along line 33 of FIG. 2;

FIG. 4 is a vector diagram showing the distribution of forces along the hydrofoil in the case in which all lifting forces are vertical and uniformly distributed along the length of the span;

FIG. 5 is a front view of an articulated hydrofoil in accordance with this invention;

FIG. 6 is a top view of the hydrofoil in FIG. 5; and

FIG. 7 is a section taken along line 77 of FIG. 5.

Referring more particularly to FIG. 1, there is illustrated in front view a hydrofoil watercraft 10 having a hull 11 attached to which is a hydrofoil structure 12 which is essentially symmetric with reference to a vertical plane on the fore and aft centerline of hull 11. Foil structure 12 includes a mounting mechanism 13 for changing the angle attack of a submerged foil 14 associated with structure 12 of the type described in copending application 546,243, filed Apr. 29, 1966, which permits foil 14 to be pivotally moved about a transverse axis approximating its hydrodynamic centerline by movement of mechanism 13 with respect to hull 11, as described in the above noted copending application. Structure 12 also includes supporting superstructure 15 fixedly attached to mechanism 13 which extends transversely of hull 11 to positions quite remote from hull 11 on each side thereof. The ends of supporting structure 15 carry the depending struts 17a and 17b, strut 17a being the starboard strut and 17b being the port strut, while just outboard of hull 11, structure 15 carries a pair of struts 18a on the starboard of hull 11 and 18b on the port. Struts 17a, 17b, 18a and 18b are preferably shaped to provide a desirable thin hydrodynamic section. Because of the bending moments of the design, struts 17a and 1712 have their thickest sections at their upper ends while struts 18a and 18b have their thickest sections intermediate their ends.

Referring also to FIGS. 2 and 3, hydrofoil 14 is in three sections, 14a, 14b and 140, spaced respectively between struts 17a and 18a, 18a and 18b, and 18b and 17b. Each section 14a, 14b and 140 is a solid, unitary structure having a metallic outer skin 19 filled with foamed polystyrene 20 and is of a length greater than a lateral spacing between particular struts 17a, 18a, 18b and 17b between which it is positioned and to the lower ends of which its ends are fixedly secured. Internally skin 19 is secured to a plurality of rods 21 which extend lengthwise of each foil 14a, 14b and 14c and are also secured at their ends to the appropriate struts 17a, 18a, 18b and 17b. Rods 21 are distributed in a manner equally to absorb spanwise stresses imposed on each foil section 14a, 14b and 140. The chordal section of foil 14 is changed along its length in a manner that the lifting forces during flight are uniformly distributed vertically along foil 14 and the hydrodynamic centerline of each foil section 14a, 14b and 14c therefore has a catenary shape.

As the chordal section of foil 14 is extremely thin to maximize hydrodynamic efliciency, since it is not required to absorb substantial bending moments, in order to prevent fluctuations in angle of attack of foil 14 along its length caused by localized vertical water movements, a series of flat vanes 22 are attached at equal distances along the span of foil 14 by means of rigid rods 23 which are secured to foil 14 and position vanes 22 in the vicinity of the streamline path of foil 14 aft of its trailing edge but out of its wash. Vanes 22 are positioned also so that they are horizontal and are not only positioned at equal intervals along the span of foil 14, but have equal areas as well.

As can be seen in the vector diagram of FIG. 4, which represents a half of a section of foil 14, for example, the outer half of section 14a, the lifting pressure produced by the water in response to the forward motion of watercraft 10, generally represented by vertical vector forces L, is distributed equally along the length of hydrofoil 14a as indicated by vectors V. Because hydrofoil section 14a is catenary shaped and incapable of developing an appreciable amount of bending moments produced by the lifting vectors V, the major portion of the upward lift L is transmitted by the hydrofoil as a tensile load T to vertical strut 17 with which the tensile load forms an angle Tensile load T is composed of vertical force L which equals T cos and equals one quarter of the portion of the weight of watercraft 10 imposed on structure 12 (assuming sections 14a, 14b and 140 are identical and struts 17a, 18a, 18b and 17b are equally spaced and symmetric with respect to the forward and aft center of hull 11), and a horizontal side load H upon strut 17a which equals T sin Because hydrofoil sections with a catenary configuration produce greater drafts than a horizontal hydrofoil for a given running submergence, in practical application it is desirable to adjust the geometrical configuration of hydrofoil sections 14a, 14b and 140 such that the angle is relatively large. The sideloads H thus produced upon struts 17a and 17b are increased with the sine of the increasing angle necessitating additional bulk for both structure 12 and struts 17a and 17b to absorb the increased sideloads. Intermediate struts 18a and 18b which only need absorb vertical loads, as each catenary foil section is identical, while the side loading on the end struts 17a and 17b is only that of the half-catenary section it supports.

Referring more particularly to FIGS. 5-7, a hydrofoil section 40 is shown positioned between and fixedly attached at its ends to the lower ends of a pair of vertical struts 37 and 38. Foil 40 can be used in place of a foil 14, in which case struts 37 and 38 would correspond to struts 17a and 17b, respectively. Foil 40 is composed of a plurality of foil sections 42 secured in position relative to one another by tensile bearing steel cables 44 passing transversely through the hydrodynamic cross sectional areas of each of sections 42. Each adjacent pair of sections 42 is separated by a cushioning layer of compressed neoprene rubber 45 to provide a uniform surface for interaction with the water while permitting hydrofoil 40 to assume a geometrical configuration approximating a catenary in response to the upward forces imposed upon hydrofoil 40 by the forward motion of watercraft 10 relative to the water. Alternatively foil sections 42 can be dove tailed without intermediate layers 45 which can be omitted, particularly when sections 42 have very small span lengths.

Each of hydrofoil sections 42 is packed with foamed polystyrene filling 47 which serves to position tensile hearing cables 44 within the sections while limiting the effect of water seepage upon the buoyancy of the craft. Cables 44 generally are located either at the hydrodynamic pressure centerline 48 or are displaced symmetrically thereabout to equalize the tensile forces carried by each of the cables. The greater flexibility associated with the articulated design of hydrofoil 40 necessitates the utilization of stabilizing hydrofoil vanes, such as vanes 22 which are optional in the case of foil 14, dependent on its thickness and aspect ratio. Hence, a number of stabilizing vanes 52 are connected to hydrofoil 40 by rods 53 as disclosed in FIG. 7. It is to be realized that the number of stabilizing hydrofoils as well as the shape of the cantenary or other are formed by the hydrofoil will vary with particular design requirements.

As shown in FIG. 7, each vane 52 is constructed to permit variation in its attack angle with respect to that of the foil section 42 to which it is attached. Thus vanes 52 can serve, not only to stabilize foil 40, but change its attitude in a long period control system.

Control of attitude of vane 52 is permitted by forming rod 53 as a hollow tube having a vertical flat 54 afiixed at its tail end, by slotting the center of the leading edge of vane 52 as indicated at 55 to receive flat 54 and by providing a central pivot pin 56 afiixed horizontally in vane 52 which is rotatably received in the appropriately central opening 57 in fiat 54. A control rod 58 which extends lengthwise in tubular rod 53 is pivotally secured at one end to vane 52 adjacent fiat 54, as indicated at 59 approximately beneath pivot pin 56, and a hydraulic control system is provided within the section 42 to which tubular rod 53 is attached to permit reciprocating movement of rod 58 in rod 53, thereby to cause vane 52 to rotate about pivot pin 56. The hydraulic control system typically includes a bellows 60 attached to the forward end of rod 58, a position sensing device 61 to sense the location of rod 58, hydraulic amplifier 62 controlled in part by position sensing device 61 as indicated by line 63 and controlled in accordance with a reference system located on the craft to which foil 40 is attached. A tube 64 is provided which extends lengthwise through foil 40 in the same manner as cables 44, except that it is extended up one of struts 37 and 38 to a master hydraulic system to supply hydraulic fluid for supplying bellows 60 through amplifier 62. Thus, when a change in the attitude of vane 52 is desired, the operator of the watercraft sends a control signal to amplifier 62 which is referenced against the position of rod 58 detected by detector 61 by means of an error detector in a conventional manner to operate amplifier 62 to admit fluid to bellows 60 from tube 64 or to exhaust fluid from bellows 60 into an exhaust return line 65 which is extended through foil 40 in the same manner as tube 64 and up to the watercraft through one of struts 37 and 38.

What is claimed is:

1. A hydrofoil structure for applying lifting force to a watercraft by the forward dynamic motion of said hydrofoil structure relative to said water comprising, a pair of support members attached to said craft transversely separated from each other, a hydrofoil of hydrodynamic crosssectional area attached at the ends thereof to said supports and having a span intermediate said supports greater than the lateral spacing of said supports, said hydrofoil having a high ratio of length to the least radius of gyration and an upwardly bowed, arcuate shape during flying operation of said watercraft such that lifting forces applied to said foil produces substantially only tensile forces in the spanwise direction of the foil.

2. A hydrofoil support according to claim 1 wherein said hydrofoil is a solid, unitary structure.

3. A hydrofoil support according to claim 1 wherein said hydrofoil is composed of a plurality of articulated, hydrodynamically shaped sections.

4. A hydrofoil support according to claim 3 wherein tensile bearing cables are passed transversely through the hydrodynamically shaped sections.

5. A hydrofoil structure according to claim 1 which further includes a vane attached to the trailing edge of said hydrofoil and positioned in the path of said hydrofoil whereby said foil senses local vertical water movements and flexes said foil where attached thereto to correct the attack angle of said foil to correct for the change therein caused by such local vertical water movement.

6. A hydrofoil structure according to claim 5 in which the attitude of said vane is controllable independently of the attitude of said hydrofoil.

References Cited UNITED STATES PATENTS 3,087,452 4/1963 Grimston 1l466.5 3,094,960 6/1963 Lang 11466.5 3,345,968 10/1967 Bailey l14'66.5

ANDREW H. FARRELL, Primary Examiner. 

